Number of compounds from the following with zero dipole moment is _________.
$$\mathrm{HF}, \mathrm{H}_2, \mathrm{H}_2 \mathrm{~S}, \mathrm{CO}_2, \mathrm{NH}_3, \mathrm{BF}_3, \mathrm{CH}_4, \mathrm{CHCl}_3, \mathrm{SiF}_4, \mathrm{H}_2 \mathrm{O}, \mathrm{BeF}_2$$
Answer (integer)
6
Solution
<p>A molecule has <strong>zero dipole moment</strong> when its <strong>bond dipoles cancel by symmetry</strong> (or when bonds are nonpolar).</p>
<table>
<thead>
<tr>
<th>Species</th>
<th>Shape (VSEPR)</th>
<th>Dipole moment?</th>
<th>Reason</th>
</tr>
</thead>
<tbody>
<tr>
<td>HF</td>
<td>linear</td>
<td>nonzero</td>
<td>polar bond, no cancellation</td>
</tr>
<tr>
<td>$\mathrm{H}_2$</td>
<td>linear</td>
<td><strong>zero</strong></td>
<td>homonuclear, nonpolar</td>
</tr>
<tr>
<td>$\mathrm{H}_2\mathrm{S}$</td>
<td>bent</td>
<td>nonzero</td>
<td>bent shape → net dipole</td>
</tr>
<tr>
<td>$\mathrm{CO}_2$</td>
<td>linear</td>
<td><strong>zero</strong></td>
<td>symmetric linear cancellation</td>
</tr>
<tr>
<td>$\mathrm{NH}_3$</td>
<td>trigonal pyramidal</td>
<td>nonzero</td>
<td>lone pair breaks symmetry</td>
</tr>
<tr>
<td>$\mathrm{BF}_3$</td>
<td>trigonal planar</td>
<td><strong>zero</strong></td>
<td>symmetric planar cancellation</td>
</tr>
<tr>
<td>$\mathrm{CH}_4$</td>
<td>tetrahedral</td>
<td><strong>zero</strong></td>
<td>symmetric tetrahedral cancellation</td>
</tr>
<tr>
<td>$\mathrm{CHCl}_3$</td>
<td>tetrahedral</td>
<td>nonzero</td>
<td>not symmetric ($3\ \mathrm{Cl}$ and $1\ \mathrm{H}$)</td>
</tr>
<tr>
<td>$\mathrm{SiF}_4$</td>
<td>tetrahedral</td>
<td><strong>zero</strong></td>
<td>symmetric tetrahedral cancellation</td>
</tr>
<tr>
<td>$\mathrm{H}_2\mathrm{O}$</td>
<td>bent</td>
<td>nonzero</td>
<td>bent shape → net dipole</td>
</tr>
<tr>
<td>$\mathrm{BeF}_2$</td>
<td>linear</td>
<td><strong>zero</strong></td>
<td>symmetric linear cancellation</td>
</tr>
</tbody>
</table>
<p>Compounds with <strong>zero dipole moment</strong>:<br>$\mathrm{H}_2,\ \mathrm{CO}_2,\ \mathrm{BF}_3,\ \mathrm{CH}_4,\ \mathrm{SiF}_4,\ \mathrm{BeF}_2$</p>
<p><strong>Number = $6$.</strong></p>
About this question
Subject: Chemistry · Chapter: Chemical Bonding and Molecular Structure · Topic: Ionic and Covalent Bonding
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